Comparison of physiological and antioxidant responses of Anoda cristata and cotton to progressive drought

Abstract

Knowledge about physiological responses of weed and crop to drought is needed to minimise crop losses caused by weed interference and to improve cropping systems and crop cultivars. In this study, gas exchange, photochemistry and antioxidant defences of two Anoda cristata (spurred anoda) accessions from Mississippi and New Mexico and two cotton types (Gossypium hirsutum and Gossypium barbadense) were evaluated under unstressed conditions and progressive drought. Under no stress, net photosynthesis (P net ) and quantum yield (F PSII ) were similar, but stomatal conductance (g s ) was higher in A. cristata than cotton. Glutathione reductase activity was highest in A. cristata from Mississippi. Cotton had at least 92% greater a-tocopherol concentration than A. cristata. Progressive drought that suppressed gas exchange to near zero decreased biomass and F PSII , but increased xanthophyll cycle conversion state in both A. cristata and cotton. Anoda cristata had prolonged gas exchange at lower leaf water contents than cotton. Air-to-leaf temperature difference was at least 66% greater in A. cristata, while a-tocopherol concentration increased only in cotton under progressive drought. Anoda cristata appears to use patchy stomatal closure and alternative electron sinks to minimise light damage during severe drought. Furthermore, sustained water-holding capacity and assimilation helped by prolonged stomatal activity, larger pigment pools and lower leaf temperature in A. cristata may confer stress tolerance and consequent success in cotton -A. cristata interference.